The present disclosure relates generally to feed control of catalysts, and more particularly, to feed control of catalysts during catalyst transition periods.
This section is intended to introduce the reader to aspects of art that may be related to aspects of the present disclosure, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
Catalysts can be employed to facilitate the formation of products through chemical reactions. It is often desirable to control and monitor the rate of chemical reactions to produce products with specific properties. For example, in polymerization reactions, the reaction rate can be controlled within specified limits to produce polymers with desired properties, such as a desired molecular weight and/or polymer chain size, among others. The reaction rate is typically affected by the amount of catalyst in the reactor, and therefore, the reaction rate can be controlled by varying the catalyst feed rate, as well as by controlling other reaction conditions.
During steady state operation, the catalyst inventory within a reactor remains fairly constant, and therefore, the overall instantaneous reaction rate, which also may remain relatively constant, can be approximated using measured process variables. For example, for polymerization reactions, the reactor catalyst inventory can be calculated by performing a laboratory test, such as an ash test to determine the fraction of catalyst in the product exiting the reactor. The fraction of catalyst in the product can be used along with the weight of solids in the reactor to calculate the reactor catalyst inventory. The calculated reactor catalyst inventory can then be used in conjunction with reaction rate constants and measured reactant concentrations to determine the reaction rate. In summary, measured variables typically can be used to determine the reaction rate during steady state operation of the reactor where the type of catalyst entering the reactor remains constant.
However, during reactor operations, there is often a need to transition from one type of catalyst to another, for example, to change over from producing one type of product to another. During catalyst transitions, process variables are continuously changing, and accordingly, it can be difficult to determine the instantaneous reaction rate. For example, during catalyst transitions, the reactor catalyst inventory and the instantaneous reaction rate can change rapidly. Accordingly, rapid adjustments may be desired to maintain the overall instantaneous reaction rate within desired limits. However, laboratory test results can take several hours to obtain, which results in lag time in the determination of the instantaneous reaction rate and the subsequent adjustment of the catalyst feed rate based on the determined instantaneous reaction rate. The lag time may cause the instantaneous reaction rate to exceed and/or fall below a desired range, which can result in product that does not meet desired product specifications (i.e., “off-spec” product). Further, an uncontrolled instantaneous reaction rate may impede reactor operations, for example, causing reactor fouling or plugging, and/or may result in slow catalyst transitions and increased catalyst waste.